1. Field of the Invention
The present invention relates to a backlight unit and a liquid crystal display (LCD) device having the same.
2. Description of the Related Art
Recently, as the semiconductor technology rapidly develops, demand for flat display devices of which the performance is further enhanced is explosively increasing.
Among the flat display devices, an LCD device recently attracts public attention. Since the LCD device has an advantage in that reduction in size and weight and low power consumption can be achieved, the LCD device has been considered as a substitute which can overcome the disadvantages of an existing cathode ray tube (CRT). Currently, the LCD is mounted on most of information processing equipments which require a display device.
A general LCD device applies a voltage to a specific molecular arrangement of liquid crystal such that the molecular arrangement is converted into a different molecular arrangement. Further, changes in optical properties of liquid crystal cells, such as birefringence, optical rotatory power, dichroism, and light scattering characteristic, are converted into visual changes. Then, the modulation of light caused by the liquid crystal cells is used to display information.
Since an LCD panel of the LCD device is a passive element which cannot emit light, the LCD panel has a backlight which provides light to the LCD panel from the lower portion of the LCD panel. Middle-sized or large-sized LCD devices such as monitors or TVs use a lamp as a backlight. The lamp not only consumes a large amount of power, but also generates heat, thereby having an adverse effect upon element characteristics of the LCD panel. Further, since the lamp is typically formed in a rod shape, the lamp is vulnerable to impact. Further, temperature deviation in each portion of the lamp is so large that an image display quality is degraded.
Meanwhile, small-sized LCD devices of mobile products such as mobile phones use a light emitting diode (LED) as a backlight. Since the LED is a semiconductor element, the LED has a long lifespan and a high lighting speed. Further, the LED has low power consumption and high impact resistance, and the reduction in size and thickness can be achieved. When the LED having such advantages is applied to middle-sized and large-sized LCD devices, it is possible to solve the above-described problems of the lamp. That is, as the LED as a point light source is modified into a line light source or surface light source, the LED can be applied to middle-sized and large-sized LCD products.
FIGS. 1A and 1B are schematic views of an LED module used as a backlight of a conventional LCD device. FIG. 1A is a cross-sectional view of the LED module, and FIG. 1B is a cross-sectional view of a bottom chassis having the LED module mounted thereon.
As shown in FIGS. 1A and 1B, the LED module 10 used as a backlight of a conventional LCD device includes a printed circuit board 13 having a plurality of LEDs 21 mounted thereon and a heat transmission member 15 attached on the rear surface of the PCB 13.
The printed circuit board 13 has electrode patterns formed thereon, the electrode patterns supplying signals to the LEDs 21. The heat transmission member 15 radiates heat generated from the LEDs 21, thereby preventing degradation of the LEDs 21.
The LED module 10 constructed in such a manner is mounted in the bottom chassis 20 having a housing space provided therein. That is, the LEDs 21 are mounted on the printed circuit board 13, and the heat transmission member 15 is attached to the rear surface of the printed circuit board 13. Then, the heat transmission member 15 is mechanically attached to the bottom chassis 20.
Therefore, the heat transmission member 15 is housed so as to be interposed between the printed circuit board 13 and the bottom chassis 20.
In the LED module 10 housed in the bottom chassis 20, however, heat transmission is not smoothly performed because of an increase in resistance caused by heat resistance of the heat transmission member 15 and a defect in contact with the bottom chassis 20.
When the heat transmission is not smoothly performed, the temperature of the LED is increased, thereby degrading the brightness. Further, the lifespan of the LEDs is reduced.